Constructs an istream iterator that is associated with stream s (the object does not own or copy the stream, only stores a reference).
The constructor may automatically attempt to extract an element from s, or defer such an operation until it is dereferenced for the first time.

(3) copy constructor

Constructs an istream iterator, with the same istream reference and current value (it does not attempt to extract an additional element on construction).

Parameters

s

A stream object, which is associated to the iterator.
Member type istream_type is the type of such stream (defined as an alias of basic_istream<charT,traits>, where charT and trais are the second and third class template parameters).